The dual wavelength optical pickup head allows to use light of different wavelengths in order to process disks of different thickness and/or different reflectivity of a reflecting layer. The dual wavelength optical pickup head may be used in most recent optical disk reading and/or writing devices, e.g. in DVD-ROM reading devices, in order to preserve a backward compatibility with older optical disk formats, e.g. a CD-R disk format. At least two characteristics of disks have to be taken into account to preserve the backward compatibility, namely a thickness and a reflectivity of the disks. DVD optical disks use a 0.6 mm thick substrate and may be read out using light with a wavelength of about 650 nm. CD-R optical disks use a substrate as thick as 1.2 mm and may be read out using light with a wavelength of about 780 nm. The CD-R optical disk has the drawback that it may not be read using light with a wavelength of about 650 nm because a special dye recovering its surface absorbs light of the latter wavelength.
A publication Dual Wavelength optical Head for 0.6 mm and 1.2 mm Substrate Thicknesses, R. Katayama, Y. Komatzu and Y. Ono, Jpn. J. Appl. Phys. Vol. 36 (1997) pp. 460-466, Part 1, No. 1B, January 1997, discloses an optical head which uses either holographic optical element type optics or variable magnification type optics. The optical head may be used with 0.6 and 1.2 mm substrate thicknesses and contains 635 nm and 785 nm laser diodes. The optical head comprises a single polarizing beam splitter and a set of signal detection optics for each 635 nm and 785 nm light beam.
Consumer product industries strive to reduce the size of their products in order to make them portable and cheaper. These efforts impose a miniaturization and/or a reduction of the number of parts in components making up the products. This would apply e.g. to the optical head of a portable and/or cheaper optical disk reading and/or writing device. On the other hand small components should be just as reliable as their more voluminous equivalents.
One aim of the present invention is to find a solution to reduce the size of an optical head without increasing its cost.